NestJS Backend Development

When to Use This Skill

Use when developing backend code in a NestJS project with TypeScript.

Recommended Project Structure

src/
├── core/
│   ├── config/              # Configuration (env validation)
│   ├── database/            # Database connections, migrations
│   ├── guards/              # Auth guards
│   ├── interceptors/        # Request/response interceptors
│   ├── filters/             # Exception filters
│   └── decorators/          # Custom decorators
├── modules/
│   └── <domain>/
│       ├── application/     # Use cases / services
│       ├── domain/          # Entities, value objects, interfaces
│       ├── infrastructure/  # Repositories, external services
│       ├── presentation/    # Controllers, DTOs, validators
│       └── <domain>.module.ts
├── shared/
│   ├── utils/
│   ├── types/
│   └── constants/
└── main.ts

Conventions

• One use case per file in application/
• DTOs with class-validator decorators in presentation/
• Repository pattern for data access in infrastructure/
• Module-scoped providers; export only what's needed

Testing

• Stack: Vitest (preferred) or Jest
• Unit test use cases with mocked dependencies
• Test file next to source: *.spec.ts
• All tests in English
• Naming: "should do X when Y"

Commands

pnpm dev          # Development with hot reload
pnpm build        # Production build
pnpm lint         # ESLint
pnpm test         # Run tests
pnpm test:cov     # Coverage report

Error Handling

• Use NestJS built-in exceptions (BadRequestException, NotFoundException, etc.)
• Custom exceptions extend HttpException
• Global exception filter for unhandled errors

Database

• Use query builder or repository pattern
• Always use transactions for multi-table writes
• Add indexes for frequently queried columns
• Use database MCPs to inspect schema before writing queries

Pre-commit Checklist

• Build passes? (pnpm build)
• Lint passes? (pnpm lint)
• Tests pass? (pnpm test)
• DTOs have proper validation?
• Error cases handled?